Encapsulation of electroluminescent devices with shaped spacers

ABSTRACT

A method of encapsulating a device is disclosed. Spacer particles are randomly located in a device region to prevent a cap mounted on the substrate from contacting the active components when pressure is applied to the cap, thereby protecting the active components from damage. The spacer particles comprise a base and an upper portion, the base being at least equal to or wider than the upper portion.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional and claims the benefit of priorityunder 35 U.S.C. Section 120 of U.S. application Ser. No. 10/065,254,filed Sep. 30, 2002, which is a continuation-in-part of U.S. applicationSer. No. 09/989,362, filed Nov. 20, 2001, which is acontinuation-in-part of International Application Serial No.PCT/SG99/00143, filed Dec. 17, 1999. The disclosure of each priorapplication is considered part of and is incorporated by reference inthe disclosure of this application.

BACKGROUND

FIG. 1 shows an OLED device 100. The OLED device comprises a substrate101, and one or more organic functional layers 102 formed between firstand second electrodes 104 and 106. The electrodes can be patterned toform, for example, a plurality of OLED cells to create a pixelated OLEDdevice. OLED cells are located in the device region where the cathodesand anodes overlap. Bond pads 110, which are coupled to the first andsecond electrodes, are provided to enable electrical connections to theOLED cells.

To protect the OLED cells from components of the environment such asmoisture and/or air, a cap 112 encapsulates the device. The activematerials of the OLED cells are sensitive and can be easily damaged dueto mechanical contact with, for example, the cap. To prevent damage tothe OLED cells, a cap or package is used. The package provides a cavity114 between the cap and OLED cells. The cavity allows for the placementof desiccant materials to cope with finite leakage rate of the device.

The demand for thin and flexible devices requires the use of thinnercomponents, such as the cap and the substrate. Decreasing the thicknessof the cap reduces its mechanical stability, making it more prone tobending, which can cause the cavity to collapse, thereby damaging theOLED cells. Spacer particles 116 are provided in the device region toprevent the cap from contacting the active components, therebyprotecting them from damage.

However, the spherical shape of spacer particles exposes the edges ofthe electrode layer 106 in regions such as region 118, to react withatmospheric components such as moisture and gases (e.g., oxygen). Thepenetration of atmospheric components into the interior of the OLED mayresult in the formation of impurities at the electrode-organic materialinterface. These impurities may cause separation of the electrode fromthe organic layer. Dark, non-emitting spots may appear at the areas ofseparation around the spacer particles due to the lack of current flow.

As evidenced from the foregoing discussion, it is therefore desirable toprovide an OLED device having improved packaging, particularly thoseformed on thin or flexible substrates.

SUMMARY OF THE INVENTION

The invention relates to encapsulation for devices, such as OLEDdevices. A cap is mounted on the substrate to encapsulate the device,forming a cavity over a device region to protect the active componentsfrom contact with the cap.

In accordance with the invention, spacer particles are provided in thedevice region to support the cap. The spacer particles are shaped toprevent the generation of dark spots around the spacer particles. Thespacer particles comprise a base and an upper portion, the base being atleast equal to or wider than the upper portion. In one embodiment, thespacer particles comprise a half-spherical shape. Spacer particlescomprising other shapes such as pyramidal, cubical, prism, or otherregular or irregular shapes, in which the base is at least equal to orwider than the upper portion, are also useful.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows an OLED device;

FIG. 2 shows one embodiment of the invention;

FIGS. 3 a-c show spacer particles according to different embodiments ofthe invention; and

FIGS. 4-8 show a process for forming an OLED device in accordance withone embodiment of the invention.

DETAILED DESCRIPTION

In one embodiment, the substrate is about 20-300 μm thick. In somecases, the thin substrate may be mechanically unstable, creatingprocessing problems. A temporary support layer (not shown) can beemployed to stabilize the substrate during the fabrication process. Thetemporary support layer, for example, can be provided on the backside ofthe substrate. In one embodiment, the temporary support layer comprisesa polymer foil coated with an adhesive for attaching to the substrate.After processing, the temporary layer is removed since the devicepackage can be used to mechanically stabilize the device.

The OLED cells comprise one or more organic layers 203 sandwichedbetween lower and upper electrodes. In one embodiment, the lowerelectrodes 204 are anodes and the upper electrodes 206 are cathodes.Forming lower electrodes that are cathodes and upper electrodes that areanodes is also useful. In one embodiment, the electrodes are patternedas strips in, for example, passive-matrix display applications.Typically, the upper and lower electrodes are patterned in first andsecond directions that are orthogonal to each other. The intersectionsof the upper and lower electrodes form the OLED cells. The cells areaddressed by activating the corresponding rows and columns.Alternatively, the OLED display comprises an active-matrix. Theactive-matrix display comprises cells that are individually addressed bythin-film-transistors (TFTs) and capacitors formed on an electronicbackplane.

A cap 210 is provided to seal the device. The cap, in one embodiment,comprises glass. Other materials, such as metal, ceramic or plastics,can also be used. The cap forms a cavity 212 that prevents damage toOLED cells caused by, for example, mechanical contact with the cap.

In accordance with one embodiment of the invention, spacer particles 208are deposited on the substrate to prevent the cap from contacting theactive components. The spacer particles are shaped to prevent the growthof dark and non-emitting spots around the particles. In one embodiment,the spacer particles comprise a base and an upper portion, the basebeing at least equal to or larger than the upper portion. The profile ofthe particles prevents regions such as 214 from being exposed topotentially deleterious components (e.g., water and oxygen) that arepresent in the device. In one embodiment, the spacer particles comprisea half-spherical shape, as shown in FIG. 2. To avoid causing shortsbetween the electrodes, the spacer particles preferably comprise anon-conductive material. In one embodiment, the spacer particles aremade of glass. Spacer particles made of other types of non-conductivematerials, such as silica, polymers, ceramic or photoresist, are alsouseful.

The average diameter of the spacer particles is preferably sufficient tomaintain the desired height of the cavity, which is, for example, about2-50 μm. The distribution of the spacer particles is preferablysufficient to ensure proper separation between the cap and OLED cellswhen mechanical pressure is applied to the device, without affecting theemission uniformity of the cells. The distribution may be varied toaccommodate design requirements, such as the thickness of the cap,thickness of the substrate, and amount of device flexibility needed.Preferably, the distribution of the spacer particles should be selectedsuch that their influence on the emission uniformity is invisible to theunaided human eye. In one embodiment, the density of the spacer particledistribution is about 10-1000 No/mm². Typically, the average distancebetween spacer particles is about 100-500 μm.

Referring to FIGS. 3 a-c, spacer particles having other geometricshapes, such as pyramidal, cubical, prism, or other regular or irregularshapes, in which the base is at least equal to or wider than the upperportion, are also useful.

FIGS. 4-8 show a process of forming an OLED device, according to oneembodiment of the invention. A first conductive layer 402 is depositedon the substrate 401. The substrate can be provided with a barrierlayer, such as silicon dioxide (SiO₂), beneath the conductive layer onthe substrate surface prior to depositing the conductive layer. Barrierlayers are particularly useful for substrates comprising soda limeglass. The barrier layer, for example, is about 20 nm thick. Varioustechniques, such as chemical vapor deposition (CVD), physical vapordeposition (PVD), and plasma enhanced CVD (PECVD), can be employed toform the device layer. The conductive layer should be thin to reduceoptical absorption and negative impact on subsequent film formationwhile satisfying electrical requirements. The conductive layer istypically about 0.02-1 μm thick.

Referring to FIG. 5, the conductive layer 402 is patterned as desired toselectively remove portions of the layer, exposing portions 504 of thesubstrate. The patterned conductive layer serves as first electrodes forthe OLED cells. In one embodiment, the conductive layer is patterned toform strips that serve as, for example, anodes of a pixelated OLEDdevice. The patterning process can also form connections for bond pads.Conventional techniques, such as photolithography and etching, can beused to pattern the conductive layer. Patterning techniques using astamp are also useful.

In accordance to the invention, shaped spacer particles 502 aredeposited on the substrate. The spacer particles, in one embodiment,comprise the desired shape before deposition. Alternatively, the spacerparticles are patterned to form the desired shape after being depositedonto the substrate. For example, the particles may be heated to a hightemperature to reflow into the desired shape on the substrate. Inanother embodiment, a photoresist is deposited on the substrate. Thephotoresist may be patterned to form the spacers with the desired shape.

In one embodiment, the spacer particles are deposited by sprayingtechniques (e.g., wet or dry spraying). Other techniques, such as spincoating, doctor blading or various printing methods (e.g., screenprinting or transfer printing) are also useful.

In a preferred embodiment, a dry spray technique is employed to depositthe spacer particles. Dry spray techniques are described in, forexample, Birenda Bahadur (Ed), Liquid Crystals: Applications and Uses,Vol. 1 (ISBN 981 02011 09). Dry spray techniques typically compriseelectrostatically charging the spacer particles with a first polarity(positive or negative) and the substrate with a second polarity(negative or positive). The spacer particles are blown against thesubstrate with dry air supplied by a dry air sprayer. Dry air sprayers,such as a DISPA-μ R from Nisshin Engineering Co., can be used.

The use of a wet spray technique to deposit the spacer particles on thesubstrate is also useful. Wet spray techniques are described in, forexample, Birenda Bahadur (Ed), Liquid Crystals: Applications and Uses,Vol. 1 (ISBN 9810201109).

In one embodiment, the spacer particles are randomly distributed on thesubstrate. The spacer particles occupy both active and non-active parts(i.e., emitting and non-emitting areas) of the device. In anotherembodiment, the spacer particles are confined to the non-active areas.Various techniques such as photolithography technology can be employedto pattern the coverage of the spacer particles. Alternatively, shadowmask or stencil mask technology can be used. A shadow mask with therequired pattern is placed in close proximity or direct contact with thesurface before deposition of the spacer particles. During the sprayapplication process, only the regions which are exposed by the mask willbe covered with spacer particles. Alternatively, a patterned dry resistfilm can be laminated on the bare surface. After the spacer particlesare deposited, the dry resist film is cured and removed from thesurface, leaving the exposed areas covered with spacer particles. Aliquid resist material can also be used in a similar manner.

The spacer particles are preferably fixed to one side of the substrateto avoid any movement. In one embodiment, the spacer particles arecoated with a thin layer of adhesive before deposition. The adhesivelayer comprises, for example, epoxy resin or acrylic resin. In oneembodiment, the adhesive is cured by heat treatment. In anotherembodiment, the adhesive is cured by exposure to ultraviolet radiation.In yet another embodiment, the adhesive comprises a hot melt material.

Referring to FIG. 6, one or more organic functional layers 602 areformed on the substrate, covering the spacer particles, the exposedsubstrate portions and conductive layer. The organic functional layerscan be formed by conventional techniques, for example, wet processessuch as spin coating or vacuum sublimation (for Alq₃ organic layers).Portions of the organic layers can be selectively removed to exposeunderlying layers in regions 604 for bond pad connections. Selectiveremoval of the organic layers can be achieved using, for example, apolishing process. Other techniques, such as etching, scratching, orlaser ablation, are also useful.

Referring to FIG. 7, a second conductive layer 704 is deposited on thesubstrate, covering the spacer particles and other layers formedthereon. In one embodiment, the second conductive layer is patterned toform electrode strips that serve as cathodes for a pixelated OLEDdevice. Also, connections for bond pads can be formed during thepatterning process. Alternatively, the conductive layer can beselectively deposited to form cathode strips and bond pad connections.Selective deposition of the conductive layer can be achieved with, forexample, mask layers. The cathode strips are typically orthogonal to theanode strips. Forming cathode strips that are diagonal to the anodestrips is also useful. The intersections of the top and bottom electrodestrips form organic LED pixels.

Referring to FIG. 8, a cap 802 is mounted on the substrate toencapsulate the device. The cap creates a cavity 803, providingseparation between it and the OLED cells. In one embodiment, a sealingframe 804 surrounding the cell region is prepared. Preparation of thesealing frame includes patterning the substrate, if necessary, to forman area for forming a sealing post 804 therein. Alternatively, thesealing frame can be formed on the cap. The height of the sealing postis sufficient to form a cavity 803 with the desired height. The use of asealing frame is described in international patent application “ImprovedEncapsulation of Organic LED Device”, PCT/SG00/00133, which is hereinincorporated by reference for all purposes.

The cap layer 802 comprises, for example, metal or glass. Other types ofcaps which protect the active components from the environment, such asceramic or metallized foil, are also useful. In yet another embodimentof the invention, the cap can be stamped or etched, depending on thematerial used, to form a cavity separating the cap and the OLED devices.

Various techniques can be used to mount the cap layer. In oneembodiment, an adhesive is used to mount the cap layer. Adhesives suchas self-hardening adhesives, UV or thermal curable adhesives, or hotmelt adhesives are useful. Other techniques which employ low temperaturesolder materials, ultrasonic bonding, or welding techniques usinginductance or laser welding are also useful.

In one embodiment of the invention, a sealing dam surrounding the deviceregion of the substrate is provided. The sealing dam supports the cap onthe substrate and provides a sealing region located at an outer face ofthe sealing dam. The use of a sealing dam is described in internationalpatent application “Sealing of Electronic Devices”, PCT/SG00/00133(attorney docket number 99E05737SG), which is herein incorporated byreference for all purposes.

During the mounting process, the spacer particles may be pressed intothe layers of the OLED cells. The spacer particles provide support forthe cap over the area of the OLED cells, preventing the cap fromcontacting the active components of the device when pressure is appliedto the cap. Bond pads 806 are formed to provide electrical access to theOLED cells.

As described, the process deposits the adhesive-coated spacer particlesafter formation of the first conductive layer. The spacer particles canalternatively be deposited at other points in the process flow. Forexample, the spacer particles can be deposited before the formation ofthe first conductive layer, before or after the formation of the secondconductive layer. In effect, the spacer particles can be deposited atany point of the process prior to mounting of the cap.

The adhesive on the spacer particles is cured at some point in theprocess flow after the deposition of the spacer particles. In oneembodiment, the adhesive is cured after the spacer particles aredeposited on the substrate and before the formation of the organiclayers. In another embodiment, the adhesive is cured after the spacerparticles are applied to the first active organic layer and before theformation of the remaining layers. In another embodiment, the adhesiveis cured after the spacer particles are applied to the second organiclayer and before the formation of the remaining layers. In yet anotherembodiment, the adhesive is cured after the spacer particles are appliedto the second conductive layer and before the encapsulation of the OLEDdevice. Spacer particles can also be useful in providing support inother types of devices that employ cavity packages. Such devicesinclude, for example, electrical devices, mechanical devices,electromechanical devices, or microelectromechanical systems (MEMS).

While the invention has been particularly shown and described withreference to various embodiments, it will be recognized by those skilledin the art that modifications and changes may be made to the presentinvention without departing from the spirit and scope thereof. The scopeof the invention should therefore be determined not with reference tothe above description but with reference to the appended claims alongwith their full scope of equivalents.

1. A method for forming a device, comprising: providing a substrate witha device region; applying a layer of adhesive on spacer particles, thespacer particles comprising a base and an upper portion, the base beingat least equal to or wider than the upper portion; depositing the spacerparticles on the substrate; curing the layer of adhesive on the spacerparticles; and mounting a cap on the substrate to encapsulate thedevice, the cap forming a cavity over the device region, wherein thespacer particles are capable of supporting the cap when pressure isapplied to the cap.
 2. The method of claim 1 wherein the devicecomprises an OLED device.
 3. The method of claim 1 wherein the spacerparticles comprise a nonconductive material.
 4. The method of claim 1wherein the step of depositing the spacer particles comprises dryspraying.
 5. The method of claim 4 wherein the spacer particles occupyactive and non-active parts of the device region.
 6. The method of claim4 wherein the spacer particles are confined to non-active parts of thedevice region.
 7. The method of claim 4 further comprising patterning aregion covered by the spacer particles using photolithography.
 8. Themethod of claim 4 further comprising using a shadow mask to define aregion covered by the spacer particles on the substrate.
 9. The methodof claim 4 further comprising defining a region covered by the spacerparticles on the substrate using dry resist patterning.
 10. The methodof claim 1 wherein the step of depositing the spacer particles compriseswet spraying.
 11. The method of claim 10 wherein the spacer particlesoccupy active and non-active parts of the device region.
 12. The methodof claim 10 wherein the spacer particles are confined to non-activeparts of the device region.
 13. The method of claim 10 furthercomprising patterning a region covered by the spacer particles usingphotolithography.
 14. The method of claim 10 further comprising using ashadow mask to define a region covered by the spacer particles on thesubstrate.
 15. The method of claim 1 wherein the step of depositing thespacer particles comprises spin coating, doctor blading, screen printingor transfer printing.
 16. The method of claim 1 wherein curing the layerof adhesive comprises thermally curing the layer of adhesive.
 17. Themethod of claim 1 wherein curing the layer of adhesive comprises curingthe layer of adhesive with ultraviolet light.
 18. The method of claim 1wherein the adhesive comprises hot melt material.
 19. A method forforming a device, comprising: providing a substrate with a deviceregion; forming a plurality of spacer particles on the substrate, thespacer particles comprising a base and an upper portion, the base beingat least equal to or wider than the upper portion; and mounting a cap onthe substrate to encapsulate the device, the cap forming a cavity overthe device region, wherein the spacer particles are capable ofsupporting the cap when pressure is applied to the cap.
 20. The methodof claim 19 wherein the step of forming a plurality of spacer particleson the substrate comprises: depositing particles on the substrate; andheating the particles to a sufficiently high temperature to cause theparticles to flow and form the spacer particles having the base that isat least equal to or wider than the upper portion.
 21. The method ofclaim 19 wherein the step of forming a plurality of spacer particles onthe substrate comprises: depositing a photoresist on the substrate; andpatterning the photoresist into the spacer particles having the basethat is at least equal to or wider than the upper portion.